1. Field of the Invention
The present invention relates to mass spectrometry systems. More particularly, it relates to mass spectrometry systems that are useful for the analysis and determination of molecules, including large and small organic molecules such as proteins or peptides, environmental pollutants, pharmaceuticals and their metabolites or degradants or impurities, food ingredients, flavor compounds, and petrochemical compounds etc., to methods of analysis used therein, and to a computer program product having computer code embodied therein for causing a computer, or a computer and a mass spectrometer in combination, to affect such analysis.
2. Prior Art
In drug metabolism studies, researchers typically create a radio-labeled version of the parent drug before dosing the drug with animal or human test subjects. Through biotransformations, the drug will be transformed into its metabolites, between just a few to as many as 50-70 metabolites. By detecting and following the radio-activity, researchers can trace these bio transformations and account for the metabolites. The sample is typically injected into an LC/MS system for analysis, where various metabolites will be separated in (retention) time and detected by mass spectrometry. While these metabolites can be traced by a radio activity detector in a split flow arrangement in parallel to mass spectrometry, the identification of these metabolites will have to rely on mass spectrometry due to its mass (m/z) measuring capability. Unfortunately in many cases, the biological sample, even after extensive clean-up, sample preparation, and LC separation, still suffers from significant matrix or background ion interferences, making metabolite identification a time-consuming and tedious process. To help with the mass spectral identification of possible metabolites, researchers may dose test subjects with a mixture of the native and radio-labeled compound, creating a unique mass spectral signature that is easier for researchers to spot in a mass spectrum. Subject to limitations on total dosage, radio-activity exposure for a given test species, mass spectral saturation, and the uncertainty surrounding the ratio between the native and the radio-labeled version of the drug, metabolite identification remains a daunting task for researchers, even with the aid of radio activity tracing.
After an ion has been possibly identified to be drug-related, it is typically required then to confirm its elemental composition before structural elucidation through further MS/MS experimentation or even isolation for NMR analysis. Due to the various backgrounds present, typically, higher resolution mass spectrometry is desired in order to avoid the interference from the matrix or background ions. Higher resolution mass spectrometry systems such as TOF, qTOF, Orbitrap, or FT ICR MS, offer two distinct advantages: less spectral interferences and higher mass accuracy. With elaborate calibration schemes such as lock mass, dual spray, and internal calibration, obtaining unique elemental composition remains a challenge even at the extremely high mass accuracy of 100 ppb.
A previous approach, as in U.S. Pat. No. 6,983,213 and International Patent Application PCT/US2005/039186, filed on Oct. 28, 2005, provides a novel method for calibrating mass spectral data to much improved mass accuracy with line shape transformation so as to enable or enhance elemental composition determination. Very high mass accuracy can be obtained on so-called unit mass resolution systems in accordance with the techniques taught in U.S. Pat. No. 6,983,213. Combined with peak shape transformation, this makes it feasible to perform elemental composition determination on even a single quadrupole mass spectrometer system. This accurate line shape calibration provides an additional metric to assist in the unambiguous formula identification by allowing for exact matching between a measured and a theoretically calculated mass spectrum for a given candidate formula, as disclosed in International Patent Application PCT/US2005/039186, filed on Oct. 28, 2005.
In spite of these later developments, obtaining unique elemental composition from even high resolution mass spectrometry systems remains a challenge to practitioners of mass spectrometry, due to the tedious calibration process involved which requires either internal or external calibration standards be measured at a time and m/z values close to those of the unknown ions.
Thus, there exists a significant gap between what the current mass spectral system can offer and what is being achieved at the present using existing technologies for mass spectral analysis.